Association of interventricular activation delay with clinical outcomes in cardiac resynchronization therapy

BACKGROUND Pacing at sites of longest interventricular delay has been associated with greater reverse remodeling in cardiac resynch-ronization therapy (CRT). However, the effects of pacing at such sites on clinical outcomes is less well studied.OBJECTIVE The purpose of this study was to assess the association between interventricular delay and clinical outcomes in CRT pa-tients implanted with quadripolar left ventricular (LV) leads.METHODS RALLY-X4 was a registry study of the Acuity X4 quadripo-lar LV leads. Interventricular delay was measured during unpaced basal rhythm from the right ventricular (RV) lead to the LV lead elec-trode (E1 to E4) chosen for CRT pacing. Patients were stratified by median RV-LV delay (80 ms) into short and long delay groups; they also were analyzed by multivariable modeling. The primary composite outcome measure was all-cause mortality and heart fail-ure hospitalization (HFH) at 18 months.RESULTS A total of 581 patients had complete RV-LV delay data. Mean LV ejection fraction was 27%, and 73% had typical left bundle branch block. Predictors of long RV-LV delay included female sex, left bundle branch block, and QRS duration .150 ms. Survival free of the primary outcome at 18-month follow-up was 87% in the long activation delay group compared with 77% in the short delay group (P = .0042). Multivariate analysis showed that RV-LV delay was an independent predictor of survival free of HFH (P = .028).CONCLUSION Among CRT patients with quadripolar LV pacing leads, longer baseline interventricular activation delay was signifi-cantly associated with the composite endpoint of all-cause mortal-ity and HFH.